Combustion and structure formation in the Ti-Ta-C-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> system

Biocompatible composites (Ti, Ta)C _x + Ca₃(PO₄)₂ for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca₃(PO₄)₂ mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have little or no influence on the burning velocity U and combustion temperature T _c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.      

Synthesis and electrochemical properties of layered LiNi<Subscript>1/2</Subscript>Mn<Subscript>1/2</Subscript>O<Subscript>2</Subscript>prepared by coprecipitation

Spherical LiNi_1/2Mn_1/2O ₂ powders were synthesized from LiOH . H₂O and coprecipitated metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The average particle size of the powders was about 10 m and the size distribution was quite narrow due to the homogeneity of the metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The tap-density of the LiNi_1/2Mn_1/2O₂ powders was approximately 2.2 g cm_–3, which is comparable to the tap-density of commercial LiCoO₂. The LiNi_1/2Mn_1/2 O₂electrode delivered a discharge capacity of 152, 163, 183, and 189 mA h g^–1 in the voltage ranges of 2.8–4.3, 2.8–4.4, 2.8–4.5, and 2.8–4.6 V, respectively, with good cyclability. Furthermore, Al(OH)₃-coated LiNi_1/2Mn_1/2O₂exhibited excellent cycling behavior and rate capability compared to the pristine electrode.     

Maximization of total surface area of Pt-SnO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst by the Taguchi method

The maximization of the total surface area of Pt-SnO₂/Al₂O₃ catalyst was studied by using the Taguchi method of experimental design. The catalysts were prepared by sol-gel method. The effects of HNO₃, H₂O and aluminum nitrate concentrations and the stirring rate on the total surface area were studied at three levels of each. L₉ orthogonal array leading nine experiments was used in the experimental design. The parameter levels that give maximum total surface area were determined and experimentally verified. In the range of conditions studied it was found that, medium levels of HNO₃ and H₂O concentration and lower levels of aluminum nitrate concentration and stirring rate maximize the total surface area.     

Structure and electrochemical characterization of LiNi<Subscript>0.3</Subscript>Co<Subscript>0.3</Subscript>Mn<Subscript>0.3</Subscript>Fe<Subscript>0.1</Subscript>O<Subscript>2</Subscript> cathode for lithium secondary battery

A lithium insertion material having the composition LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ was synthesized by simple sol-gel method. The structural and electrochemical properties of the sample were investigated using X-ray diffraction spectroscopy (XRD) and the galvanostatic charge-discharge method. Rietvelt analysis of the XRD patterns shows that this compound can be classified as α-NaFeO₂ structure type (R3m; a=2.8689(5) Å and 14.296(5) Å in hexagonal setting). Rietvelt fitting shows that a relatively large amount of Fe and Ni ion occupy the Li layer (3a site) and a relatively large amount of Li occupies the transition metal layer (3b site). LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ when cycled in the voltage range 4.3–2.8 V gives an initial discharge capacity of 120 mAh/g, and stable cycling performance. LiNi_0.3Co_0.3Mn_0.3Fe_0.1O₂ in the voltage range 2.8–4.5 V has a discharge capacity of 140 mAh/g, and exhibits a significant loss in capacity during cycling. Ex-situ XRD measurements were performed to study the structure changes of the samples after cycling between 2.8–4.3 V and 2.8–4.5 V for 20 cycles. The XRD and electrochemical results suggested that cation mixing in this layered structure oxide could be causing degradation of the cell capacity.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> xerogel support on hydrogen production by steam reforming of LNG over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-ZrO<Subscript>2</Subscript> catalyst

An Al₂O₃-ZrO₂ xerogel (AZ-SG) was prepared by a sol-gel method for use as a support for a nickel catalyst. The Ni/AZ-SG catalyst was then prepared by an impregnation method, and was applied to hydrogen production by steam reforming of LNG. A nickel catalyst supported on commercial alumina (A-C) was also prepared (Ni/A-C) for comparison. The hydroxyl-rich surface of the AZ-SG support increased the dispersion of nickel species on the support during the calcination step. The formation of a surface nickel aluminate-like phase in the Ni/AZ-SG catalyst greatly enhanced the reducibility of the Ni/AZ-SG catalyst. The ZrO₂ in the AZ-SG support increased the adsorption of steam onto the support and the subsequent spillover of steam from the support to the active nickel sites in the Ni/AZ-SG catalyst. Both the high surface area and the well-developed mesoporosity of the Ni/AZ-SG catalyst improved the gasification of adsorbed surface hydrocarbons in the reaction. In the steam reforming of LNG, the Ni/AZ-SG catalyst showed a better catalytic performance than the Ni/A-C catalyst. Moreover, the Ni/AZ-SG catalyst showed strong resistance toward catalyst deactivation.     

Preparation and Characterization of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> Synthesized by an Emulsion Drying Method

A layered LiNi_0.8Co_0.2O₂ solid solution, which is a promising cathode material for secondary lithium batteries, was successfully synthesized by an emulsion drying method. Because electrochemical properties significantly depend on the conditions of the synthesis, the calcination temperature was carefully determined on the basis of X-ray diffraction and TG studies. The prepared cathodes were characterized by means of SEM, BET, X-ray diffraction, Rietveld refinement, cyclic voltammetry and a charge-discharge experiment. From the Rietveld analysis, it was found that powder calcined at 800 °C for 12 h exhibits a well ordered and lower cation mixed layered structure than the others. The cyclic voltammetry experiment shows that phase transformation can be suppressed considerably by increasing the calcination temperature to 800 °C. The highest discharge capacity of 188.4 mA h g⁻¹ was obtained from the sample prepared at 800 °C. Furthermore, a high capacity retention ratio of 88.1% was found for the initial value after 50 cycles at a constant current density of 40 mA g⁻¹ between 2.7 V_Li/Li⁺ and 4.3 V_Li/Li⁺. In the rate capability test, the cathode delivered a higher discharge capacity of 153.1 mA h g⁻¹ at a 4 C (800 mA g⁻¹) rate.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Self-Metathesis of 1-Octene Using Alumina-Supported Re<Subscript>2</Subscript>O<Subscript>7</Subscript> in Supercritical CO<Subscript>2</Subscript>

In this contribution we describe the use of heterogeneous catalysts for the liquid-phase self-metathesis of 1-octene in supercritical CO₂. Our work aims at addressing the mass-transfer problems associated with such reaction systems. By coupling a heterogeneous supported Re₂O₇ catalyst with the use of scCO₂, the self-metathesis of 1-octene takes place by and large much more rapidly than in traditional solvent media, and furthermore, by using scCO₂ the overall efficiency and sustainability of the transformation can be improved.

Side-by-Side In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanotubes: Synthesis and Optical Properties

A simple and mild wet-chemical approach was developed for the synthesis of one-dimensional (1D) In(OH)₃ nanostructures. By calcining the 1D In(OH)₃ nanocrystals in air at 250 °C, 1D In₂O₃ nanocrystals with the same morphology were obtained. TEM results show that both 1D In(OH)₃ and 1D In₂O₃ are composed of uniform nanotube bundles. SAED and XRD patterns indicate that 1D In(OH)₃ and 1D In₂O₃ nanostructures are single crystalline and possess the same bcc crystalline structure as the bulk In(OH)₃ and In₂O₃, respectively. TGA/DTA analyses of the precursor In(OH)₃ and the final product In₂O₃ confirm the existence of CTAB molecules, and its content is about 6%. The optical absorption band edge of 1D In₂O₃ exhibits an evident blueshift with respect to that of the commercial In₂O₃ powders, which is caused by the increasing energy gap resulted from decreasing the grain size. A relatively strong and broad purple-blue emission band centered at 440 nm was observed in the room temperature PL spectrum of 1D In₂O₃ nanotube bundles, which was mainly attributed to the existence of the oxygen vacancies.     

Time-resolved X-ray diffraction study of SHS-produced NiAl and NiAl-ZrO<Subscript>2</Subscript> composites

NiAl and NiAl-ZrO₂ intermetallic composites were prepared from pressed elemental powders by SHS in a dynamic vacuum. The effect of diluent properties (such as conductivity and grain size) on the parameters of the SHS reaction has been investigated by time-resolved X-ray diffraction (TRXRD). By decreasing the reactivity of the green mixture, these nonreactive additives not only slow down the velocity of combustion front propagation but can also give rise to local melting of the product. Synchrotron radiation was also used to elucidate the reaction mechanism. It has been found that the combustion synthesis of NiAl is triggered by aluminum melting and proceeds via the formation of two transient intermetallic phases, NiAl₃ and Ni₂Al₃. In the final product, only the NiAl phase has been detected.      

Effects of preparation methods for V<Subscript>2</Subscript>O<Subscript>5</Subscript>-TiO<Subscript>2</Subscript> aerogel catalysts on the selective catalytic reduction of NO with NH<Subscript>3</Subscript>

A series of V₂O₅-TiO₂ aerogel catalysts were prepared by the sol-gel method with subsequent supercritical drying with CO₂. The main variables in the sol-gel method were the amounts of V₂O₅ and when the vanadium precursor was introduced. V₂O₅-TiO₂ xerogel and V₂O₅/TiO₂ (P-25) were also prepared for comparison. The V₂O₅-TiO₂ aerogel catalysts showed much higher surface areas and total pore volumes than V₂O₅-TiO₂ xerogel and impregnated V₂O₅/TiO₂ (P-25) catalysts. The catalysts were characterized by N₂ physisorption, X-ray diffraction (XRD), FT-Raman spectroscopy, temperature-programmed reduction with H₂ (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The selective catalytic reduction of NOx with ammonia in the presence of excess O₂ was studied over these catalysts. Among various V₂O₅-TiO₂ catalysts, V₂O₅ supported on aerogel TiO₂ showed a wide temperature window exhibiting high NOx conversions. This superior catalytic activity is closely related to the large amounts of strong acidic sites as well as the surface vanadium species with characteristics such as easy reducibility and monomeric and polymeric vanadia surface species. This work was presented at the 7 ^th Korea-China Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

SHS quenching as a route to bulk glassy Fe<Subscript>34</Subscript>Co<Subscript>34</Subscript>B<Subscript>10</Subscript>Si<Subscript>14</Subscript>Nb<Subscript>8</Subscript> alloys

The method of SHS quenching combined with dynamic annealing was used to prepare bulk amorphous metallic glass alloys Fe₃₄Co₃₄B₁₀Si₁₄Nb₈ in a two-stage process. The structural properties and microstructure of thus prepared materials were found to be close to those produced by other methods, such as melting-injection-molding and melt spinning.      

Selective oxidation of H<Subscript>2</Subscript>S to ammonium thiosulfate and elemental sulfur using mixtures of V-Bi-O and Sb<Subscript>2</Subscript>O<Subscript>4</Subscript>

The selective oxidation of hydrogen sulfide in the presence of excess water and ammonia was investigated by using vanadium-bismuth based mixed oxide catalysts. Synergistic effect on catalytic activity was observed for the mechanical mixtures of V-Bi-O and Sb₂O₄. Temperature programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS), and two separated bed reactivity test results supported the role of Sb₂O₄ for reoxidizing the reduced V-Bi-O during the reaction. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Trapping characteristics of volatile ruthenium oxides by Y<Subscript>2</Subscript>O<Subscript>3</Subscript> filter

Yttria filter has been suggested as a trapping agent for gaseous oxides of ruthenium volatilized during DUPIC fuel fabrication process. Experiments were performed to evaluate the trapping characteristics of gaseous ruthenium oxides by yttria ceramic foam filters in the two-zone furnace under air condition. Yttria filter is expected to offer stable material in which the volatility of the ruthenium can be effectively trapped because of its incorporation into a lattice of high stability over 900 ‡C under air condition. The XRF result of ruthenium trapped on an yttria filter under air condition showed that concentrations of ruthenium on the back and the front faces of the filter decreased linearly with increasing superficial air velocity, and the back face concentration of filter was lower than the front face concentration by about 30-45%. The TGA result of ruthenium trapped on an yttria filter indicates that there is weight loss of 5.8 wt% up to 1,400 ‡C, which is believed to be due to the fact that the thermally stable Y₂Ru₂O₇ phase was formed on an yttria filter.     

Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Synergism Between Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Au/TiO<Subscript>2</Subscript> in the Low Temperature Oxidation of Propene

CO impedes the low temperature (<170 °C) oxidation of C₃H₆ on supported Pt. Supported Au catalysts are very effective in the removal of CO by oxidation, although it has little propene oxidation activity under these conditions. Addition of Au/TiO₂ to Pt/Al₂O₃ either as a physical mixture or as a pre-catalyst removes the CO and lowers the light-off temperature (T ₅₀) for C₃H₆ oxidation compared with Pt catalyst alone by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.     

Partial oxidation of methane over Ni/Ce-Zro<Subscript>2</Subscript>/θ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The catalytic behavior of Ni/Ce-ZrO₂/θ-Al₂O₃ has been investigated in the partial oxidation of methane (POM) toward synthesis gas. The catalyst showed high activity and selectivity due to the heat treatment of the support and the promotional effect of Ce-ZrO₂. It is suggested that the support was stabilized through the heat treatment of γ-Al₂O₃ and the precoating of Ce-ZrO₂, on which a protective layer was formed. Moreover, sintering of the catalyst was greatly suppressed for 24 h test. Pulse experiments of CH₄, O₂ and/or CH₄/O₂ with a molar ratio of 2 were systematically performed over fresh, partially reduced and well reduced catalyst. Results indicate that CH₄ can be partially oxidized to CO and H₂ by the reactive oxygen in complex NiO_x species existing over the fresh catalyst. It is demonstrated that POM over Ni/Ce-ZrO₂/θ-Al₂O₃ follows the pyrolysis mechanism, and both the carbonaceous materials from CH₄ decomposition over metallic nickel and the reactive oxygen species present on NiO_x and Ce-ZrO₂ are intermediates for POM.     

The Oxidative Polycondensation of Benzylidene-4′-hydroxyanilene using Air O<Subscript>2</Subscript>, NaOCl and H<Subscript>2</Subscript>O<Subscript>2</Subscript>: Synthesis and Characterization

In this work, the oxidative polycondensation reaction conditions of benzylidene-4′-hydroxyanilene (B-4′-HA) were studied using oxidants such as air O₂, H₂O₂ and NaOCl in an aqueous alkaline medium between 40 and 95 ^○C. Oligo-benzylidene-4′-hydroxyanilene was characterized by ¹H-NMR, FT-IR, UV-Vis, size exclusion chromatography (SEC) and elemental analysis techniques. The solubility of oligomer using organic solvents such as DMF, THF, DMSO, methanol, ethanol, CHCl₃, CCl₄, toluene, acetonitrile, ethyl acetate was investigated. According to air O₂ oxidant (flow rate 8.5 L/h), the conversion of B-4′-HA was 82.0% in optimum conditions such as [B-4′-HA]₀=[KOH]₀=0.1015 mol/L at 50 ^○C for 25 h. According to the SEC analysis, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values of O-B-4′-HA were found to be 1852 g mol⁻¹, 3101 g mol⁻¹ and 1.675; 2123 g mol⁻¹, 4073 g mol⁻¹ and 1.919; 2155 g mol⁻¹, 4164 g mol⁻¹ and 1.932, using air oxygen, NaOCl and H₂O₂ oxidants, respectively. Also, Thermo gravimetric analysis (TGA) showed oligo-benzylidene-4′-hydroxyanilene to be unstable against thermo-oxidative decomposition. The weight loss of O-B-4′-HA was found to be 95.87% at 1000 ^○C.     

Preparation of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> hollow spheres and their activity in methylene blue photodecomposition

PSA [poly-(styrene-methyl acrylic acid)] latex particle has been taken into account as template material in SiO₂ hollow spheres preparation. TiO₂-doped SiO₂ hollow spheres were obtained by using the appropriate amount of Ti(SO₄)₂ solution on SiO₂ hollow spheres. The photodecomposition of the MB (methylene blue) was evaluated on these TiO₂-doped SiO₂ hollow spheres under UV light irradiation. The catalyst samples were characterized by XRD, UV-DRS, SEM and BET. A TiO₂-doped SiO₂ hollow sphere has shown higher surface area in comparison with pure TiO₂ hollow spheres. The 40 wt% TiO₂-doped SiO₂ hollow sphere has been found as the most active catalyst compared with the others in the process of photodecomposition of MB (methylene blue). The BET surface area of this sample was found to be 377.6 m²g⁻¹. The photodegradation rate of MB using the TiO₂-doped SiO₂ catalyst was much higher than that of pure TiO₂ hollow spheres.     

Rhodium stabilized Prussian Blue-modified graphite electrodes for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

Graphite electrodes chemically modified with Prussian Blue (G/PB) were obtained by spreading, on the electrode surface, appropriate volumes of 100 mM K₃[Fe(CN)₆] and 100 mM FeCl₃ solutions, both containing 10 mM HCl. In order to improve the electrochemical response stability, the potential of G/PB electrodes was cycled (in the domain where PB exhibits electrochemical activity) in 0.1 M KCl solution (G/PB-K), as well as in 2 mM RhCl₃ solution, containing 0.05 M KCl (G/PB-Rh). Compared with G/PB-K, the G/PB-Rh modified electrodes showed: (i) higher relative stability of the PB electrochemical response; (ii) better analytical parameters for H₂O₂ amperometric detection; (iii) slightly lower rate constant corresponding to the second order electrocatalytic reaction for H₂O₂ amperometric detection; (iv) an electrocatalytic activity not affected by the H₂O₂ concentration.